Process for preparation and separation of light sensitive stabilized diazo resins



Dec. 17, 1968 J UL ET AL 3,417,055

PROCESS FOR PREPARATION AND SEPARATION OF LIGHT SENSITIVE STABILIZED DIAZO RESINS Original Filed Feb. 27, 1964 2-- HYDROPH/L/C ,LA YER /A l m a m sx osso STABILIZED 0/4 20 RES/N 2 HYDROPH/L/C LAYER GRA INED A L UM/NUM JAMES E HOULE G/LOEN R. VAN NORMAN INVENTORS ATTORNEY 8 AGENT United States Patent 3,417,055 PROCESS FOR PREPARATION AND SEPARATION OF LIGHT SENSITIVE STABILIZED DIAZO RESINS James F. Houle and Gilden R. Van Norman, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Continuation of application Ser. No. 347,931, Feb. 27, 1964, now Patent No. 3,342,601, dated Sept. 19, 1967. This application June 22, 1967, Ser. No. 648,036

4 Claims. (Cl. 26072.5)

ABSTRACT OF THE DISCLOSURE Stabilized diazo compositions for use in preparing lithographic printing plates are described. The compositions are particularly useful for coating on hydrophilic layers containing certain titanium complexes.

This application is a continuation application of US. application Ser. No. 347,931, filed Feb. 27, 1964, the entire subject matter of which is hereby incorporated by reference.

This invention relates to lithographic printing plates, more particularly to offset printing plates commonly used in the lithographic trade.

Lithographic plates are well known in the graphic arts field, particularly those having metal supports such as aluminum or zinc. In recent years aluminum has been particularly attractive for lithographic plates due to its cost, availability and light weight. However, when aluminum is used as a substrate for printing plates, certain inherent disadvantages must first be overcome. For instance, it has been established that the naturally occurring oxide film on aluminum is not sufficiently hydrophilic to provide trouble-free operation on a lithographic printing press. The bare aluminum is prone to become slightly hydrophobic or oleophilic resulting in a gradual buildup of ink on the non-printing areas. This phenomena is referred to in the trade as toning or scumming. In

order to eliminate toning or scumming, a suitable, permanently hydrophilic surface which is relatively insoluble must be provided. Aluminum is also know to react with certain sensitive materials, such as diazo resins coated thereon, as indicated in US. Patent 2,714,066.

Several methods of imparting an insoluble, permanently hydrophilic surface to the aluminum substrate have been suggested in the prior art. Typical treatments include anodizing, coating the surface with a hydrophilic organic polymer, etc.

Another method of providing an aluminum plate having an insoluble, hydrophilic layer which also isolates the diazo light-sensitive coating from the aluminum substrate is to deposit a coating on the aluminum of a silicate containing the SiO radical. Such a plate has limited press life and also is subject to decreases in contrast during storage. It has been desirable to provide a plate having greater press latitude, longer press life and longer shelf life than provided by the plates of the prior art. To achieve improved characteristics for a presensitized plate, it is desirable to obtain a plate having a grained surface, an improved method of treatment to provide a hydrophilic surface, and a stabilized light-sensitive coating thereon, thus giving a combination of superior printing and keeping qualities.

One object of this invention is to provide hydrophilic lithographic printing surfaces. Another object is to provide a presensitized lithographic printing plate. A further object is to provide a diazo sensitized, grained aluminum, lithographic printing plate. A further object is to provide a method for the preparation of stabilized, presensitized Patented Dec. 17, 1968 "ice diazo resins. Other objects will be apparent from the following disclosure.

The above objects and other objects are attained by coating a stabilized, light-sensitive diazo resin which has been isolated from strong acid by: (1) treating the resin solution with a cadmium salt to form a mixture cadmium salt of the resin in the strong acid and (2) subsequently treating the resulting resinous salt-acid mixture with a soluble salt, the cation of which will precipitate with any undesirable acid anion; on a lithographic support, especially a grained aluminum lithographic printing plate which has been treated with a substantially water soluble titanium compound.

A useful source of the titanium compound for treatment of the plate support is the titanium ortho-esters such as, for example, the tetraalkyl titanates. Although other titanates may be used, the preferred tetraalkyl titanates are those having alkyl groups with 2 to 5 carbon atoms such as, for example, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisobutyl titanate, tetraamyl titanate, etc.

The acidic constituent which is useful for reacting with the titanate produces a water-soluble titanium complex in an acid media. Useful acidic constituents include, for example, fluosilicic acid, hydrofluoric acid, phosphoric acid, fluoboric acid, etc. The composition for the titanium compound treatment is preferably prepared by adding the alkyl titanate which immediately reacts to form hydrous titanium dioxide which subsequently dissolves and/or reacts forming a so-called basic titanium salt. Further details of the treatment and compositions therefore are found in US. application Ser. No. 347,931 mentioned above.

The light-sensitive coating may be a suitably stabilized water-soluble resin containing the diazonium group which upon exposure to ultraviolet light forms an oleophilic surface or image.

The light-sensitive coating may be of the general Where X is chlorine;

M is a di or trivalent metal of the groups known to stabilize the diazonium groups, e.g. cadmium, zinc, bismuth, arsenic, antimony, tin, iron, platinum, mercury;

X is an anion or mixture of anions consisting of halogen or sulfates;

Z may be a phenyl or substituted phenyl in which case the resin is an aldehyde condensation product of a p-diazodiphenylamine salt. In this case, Y 'is hydrogen. Z and Y may also be organic radicals functionally capable of entering into an addition polymerization, polyesterification, condensation or other reaction capable of producing a relative low molecular weight resin or capable of reacting with a preformed polymer. Z and Y in this case may be the same or different, the parent diazonium compound being a substituted p-diazo aniline.

Some examples of the reactive groups are hydroxyl as in N ethyl N ([3 hydroxyethyl)-anilino, 4-diazo salts capable of reacting with polymerizable groups such as acryloyl, methacryloyl, etc.

The placement of various groups on the anilino nitrogen can result in the preparation of polyesters, polyethers, polyurethanes, polyacetals, polycarbonzates, etc., by direct polymerization or condensation with functionally proper preformed polymers.

In a preferred embodiment, the light-sensitive coating consists of an aldehyde condensation product of a p-diazo diphenyl amine. Light-sensitive aldehyde condensation products of p-diazo diphenyl amine stabilized with metal salts are well known in the art as described in US. Patent 2,714,066. Such resins are also available commercially, e.g., Diazo Resin No. 4. This material is described as a diazonium sulfate-zinc chloride double salt. However, as stated in the prior art, aluminum reacts with the diazo resin causing decomposition. Therefore, in a preferred embodiment we use a method of preparation and stabilization of the light-sensitive diazo resins such that they are not decomposed by the aluminum surface. For example, a suitable-resin is prepared by mixing a diazoaniline salt and an aldehyde together thoroughly in the dry state, adding the resultant mixture in portions to a strong acid such as sulfuricacid while keeping the temperature below about 5 C., contacting the reaction mixture with a cadmium compound to form the cadmium salt of the diazoanilinealdehyde condensation product, adding an excess (based on the amount of acid present) of a soluble salt, e.g., barium chloride, which will precipitate the undesirable acid anion, e.g., sulfate as barium sulfate. The precipitate, containing the cadmium salt of diazo-aldehyde resin and barium sulfate, can then be extracted to give a solution containing the cadmium salt of the resin which can then be dried. It is especially advantageous, however, to extract the precipitate with hydrofluoric acid to remove residual soluble barium ions as a precipitate of barium fluoride. This step results in a resin free from contaminating cations and upon further addition of a cadmium halide, e.g., cadmium chloride, results in a resin of higher cadmium salt content. Additional steps such as using a lower alkanol, e.g., isopropanol, in the extraction procedures tend t reduce the water content of the resin on drying and thereby further stabilize the resin.

The presensitized, grained aluminum printing late prepared according to our specifications, may be handled and treated in use as is customary in the art. The unexposed areas are removed and the plate lacquered, after which the plate is used on a lithographic printing press.

The sensitive layer for the lithographic plate can be exposed to visible light, ultraviolet light, infrared light, X-rays or to heat patterns in order to form differential areas for printing. It is possible to use light-sensitive organic compounds such as aliphatic and aromatic esters, hydrazides and amides of naphthoquinone-diazide-sulfonates, cinnamalonic acids, their substitution products and functional derivatives, diazonium salts of amino-diphenyl amines and their condensation products with formaldehyde, orthoand paraquinone diazides of benzals, anthracenes and heterocyclic systems, for example, quinoline, indazoles, benzimidazoles, diphenyloxides, also diazoketones, unsaturated ketones, orthoand paraiminoquinone diazides, derivatives of alkylnitronaphthalenesulfonates, nitroaldehydes, acenaphthene, stilbene, azides and diazides and high molecular polymer diazo resins. Silver halide emulsions may also be used. Moreover, the subbing may be overcoated with a photoconductive layer havin a high electrical resistance which can be charged and subsequently discharged by light or heat as in electrophotography, for example, low or high molecular weight organic photoconductors, also mixtures thereof with resins. Particularly suitable as photoconductors are oxadiazoles, imidazolones, triazole, oxazole, thiazoles, hydrozones, triazines, polyvinyl carbazole and polyvinyl oxazoles.

Useful resins may contain groups which tend to make the resins soluble in alkali, such groups include acid anhydride, carbonic acid, sulfonic acid, sulfonamide and sulfonimide groups, for example, polyvinyl polymers or mixed vinyl polymers, phthalic acid ester resins, alkyl resins, rosins and polyacrylic acid resins.

The lithographic plates of the invention are further characterized by good adhesion and produce good removal of the unexposed areas so that they can produce a large number of copies.

The drawing shows one embodiment of our invention.

FIG. 1 shows a grained aluminum sheet 3 having thereon a hydrophilic layer produced by treatment with a titanyl salt complex 2 and having thereon a light-sensitive stabilized diazo resin 1.

FIG. 2 shows the structure of FIG. 1 following exposure to light and removal of the unexposed areas of the stabilized diazo resin.

The following examples are intended to illustrate our invention but not to limit it in any way.

Example 1.-Titanyl silicofluoride A sheet of brush-grained aluminum having a thickness of 5 mils is immersed in a solution of titanium complex prepared by agitating vigorously a solution of 750 ml. of distilled water in 50 ml. of 31.9% fluosilicic acid, while 10 ml. of tetraisopropyl titanate is added rapidly in a fine stream. The aluminum is then passed between two mechanically driven inch diameter rubber rolls under sufficient pressure to remove the excess solution. A very thin film of solution is thus obtained which dries rapidly at room temperature. Similar coatings are obtained on other supports including polymeric materials, paper, metal, etc.

Example 2.Titanyl peroxy phosphate To 740 ml. of water is added 10 ml. (16.9 g.) of phosphoric acid (0.1588 mol) and 30 ml. (33 g.) of 28% hydrogen peroxide (0.262 mol). Then with good agitation 10 ml. (9.55 g.) of tetraisopropyl titanate (0.0336 mol) is added. The result is an orange-yellow solution which is ready for coating. This solution is coated as in Example 1 to give a thin coating on the surface of the support.

Example 3.Preparation of a titanyl fluoborate coating solution To 750 ml. water is added 14.7 g. (0.0672 mole) of 40% fluoboric acid with sufficient stirring to mix. To this solution 10.0 ml. (0.0336 mole) of tetraisopropyl titanate is added with good agitation. The ortho-ester hydrolyzes immediately forming a white precipitate which gradually redissolves forming a clear solution. This solution is then coated on a grained aluminum sheet, dried, and sensitized with a dilute aqueous solution of diazo resin as in Example 5. When properly exposed and processed, as in Example 6, the titanyl fluoborate solution produces a suitable hydrophilic printing surface. Similar coatings are obtained on the supports of Example 1.

Example 4.Preparation of a pertitanic acid coating composition Tetraisopropyl titanate is added to a dilute aqueous solution of hydrogen peroxide in the same manner as the previous example. The white hydrolysis product rapidly turns yellow and gradually dissolves to produce a clear yellow solution. A particularly useful composition for application as in Example 1 contains 0.045 mol/l. of titanium and 0.307 mole/l. of hydrogen peroxide. The hydrophilic character of the surface obtained is enhanced by drying at an elevated temperature. Similar coatings are obtained on the supports of Example 1.

Example 5.-Diazo resin A diazo resin is prepared by mixing 34 g. p-diazo diphenyl amine sulfate-zinc chloride double salt with g. concentrated sulfuric acid which has been cooled to a temperature of 10 C. The mixture is agitated while the temperature is maintained at less than 3 C. while 3.25 g. para-formaldehyde, and 6.05 g. anhydrous cadmium chloride are added. The viscosity increases over a period of approximately one-half hour and the mixture becomes homogenous. The mixture is then poured over g. of ice and stirred until the ice melts, the yellow precipitate is filtered, redissolved in water and reprecipitated into two liters of isopropyl alcohol, filtered and dried under a vacuum in the dark. Twenty-eight grams are obtained. This resin is a stabilized diazo resin.

Example 6 The treated, grained aluminum of Examples 1 and 2 is then sensitized by immersing in a dilute 2%, aqueous solution of diazo resin, passed between two rubber rolls to remove the excess and dried. When exposed at approximately 24 inches through a negative with a high intensity 220 volt carbon arc in a Nu Arc Printer, the exposed portions are hardened.

The unexposed portions of the diazo resin are removed by washing with water. The image is then lacquered with a commercially available image lacquer.

The plate is then put on the lithographic printing press and produces 90,000 satisfactory copies.

Example 7.Preparation of a preferred diazo resin sensitizer An 800 ml. beaker is equipped with a mechanically driven propeller type stirrer and external cooling is provided. To the reaction vessel is added 540 g. (5.35 moles) of 96% sulfuric acid followed by portion-wise addition of 138 g. (0.377 mole) of Sensitizer DP (para diazo diphenyl amine sulfate-zinc chloride double salt) with stirring at to C. until solution is complete. The mixture is then cooled and maintained at 0 C. during the gradual addition of 100 ml. (0.592 mole) of fluoboric acid followed by the addition of 13.0 g. (0.432 mole) paraformaldehyde with vigorous agitation to provide rapid and uniform dispersion of the paraformaldehyde. An additional 100 ml. (0.592 mole) 40% fluoboric acid is then added. The resultant mixture is now deep red in color Whereas prior to the initial addition of fluoboric acid the solution was brownish in color. The reactant mixture is stirred and maintained at 0 C. for a period of one hour and ten minutes whereupon it is poured with good agitation into 800 g. ice containing 210 ml. (1.24 moles) of 4% fluoboric acid. The precipitate which forms is then filtered and collected. The moist cake is then dissolved in 700 ml. dimethylformamide and refiltered. The clear filtrate is then agitated during the addition of 220 :g. (0.965 mole) of cadmium chloride (CdCl -2 /2H O) dissolved in 250 ml. Water. The precipitate thus formed is filtered and collected. The moist cake is then added to 2 liters of isopropyl alcohol and stirred vigorously to produce a small uniform particle size slurry. The slurry is filtered, collected and formed again in the same manner as above in 1 liter of diethyl ether. The slurry is then filtered, collected and dried under vacuum at room temperature, care being taken to break up the moist cake to provide uniform drying. The yield of dry resin is 100 g. in the form of a light orange-yellow powder.

Example 8.Preparation of a diazo resin sensitizer II In a 1,500 ml. glass beaker was placed 1,040 of 96% sulfuric acid. The beaker was suspended and equipped with a variable speed stirrer. The stirring acid was cooled below 0 C. with a Dry Ice-acetone bath.

A 272 g. portion of Fairmount DP salt (paradiazo diphenyl amine sulfate-zinc chloride double salt) and 26 g. of paraformaldehyde were mixed together thoroughly in the dry state and then added in portions to the acid, keeping the temperature below 5 C. The addition took 10 minutes. Stirring was continued for 75 minutes, keeping the temperature below 0 C.

The acid solution was poured over a mixture of 2,200 g. of crushed ice and a solution of 1 lb. of cadmium chloride in 600 ml. of water with good agitation. A 3 liter portion of isopropyl alcohol was added and the resultant slurry filtered. The precipitate was slurried in 4 liters of water and 3 moles (624 g.) of barium chloride added. The resultant precipitate was filtered off and subsequently extracted twice with 3 liter portions of 0.75 M HF solution and a third time with 2 liters of distilled water. The filtrates were combined and a solution of 1 lb. of

6 cadmium chloride in 400 ml. added. Then 8 liters of isopropyl alcohol were added and the slurry filtered. The product was dried under vacuum at room temperature. The yield was 286 g.

Example 9 When the stabilized diazo resins of Examples 7 and 8 are coated on to untreated grained aluminum sheet, they are found to have better stability on aging than similar coatings made using diazo materials prepared by previously known methods. The stability is particularly better when the diazo resins are coated on a support carrying a layer of the mentioned titanium complexes.

It will be appreciated that while aluminum alloys are intended to be within the scope of our invention as well as metal laminates.

The solutions used to remove the unhardened areas of the diazo resin are not critical. Water may be used, but aqueous gum solutions known in the art are also useful. It will be appreciated that other lacquers available commercially may also be used.

The diazo resins which may be used in our invention are prepared, stabilized and used in the dark or under yellow light. Therefore, when these resins are coated'on the treated plate, the coating operation is carried out under appropriate safelight conditions.

Example 10 The treated grained aluminum of Examples 1 and 2 is sensitized by coating with light-sensitive polymers using the whirler coating technique. Kodak Photo Resist yields a clean appearing image. When inked, 50 press copies are obtained on the lithographic press. Kodak Metal Etch Resist is developed by tray development followed by water wash-off and compressed air dried down to yield a robust, clean appearing image. The image is resistant to prolonged rubbing. Light sensitive compositions of the type described in US. patent 2,948610 are swab developed with 0.5% sodium carbonate to yield adherent,

' ink-receptive images. Azoplate Positop developed with Positop developer yields adherent robust images which show good press life. Light-sensitive polycarbonate resins of the type described in U.S. patent 3,043,802 are tray developed to yield clean, ink-receptive images. A negative working wash-off light-sensitive silver halide emulsion is transferred to the treated surface from the strippable support. After activation, the untanned gelatin is washed off.

A light-sensitive silver halide emulsion comprising the first gelatin layer containing an oxidizing developer and a second layer containing light-sensitive silver halide is coated on the treated support. A satisfactory lithographic plate is obtained after activation and inking of the surface.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be elfected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A process for preparing a stable, light-sensitive diazo resin, said process comprising:

(a) thoroughly mixing about 1 part by weight paraformaldehyde together with about 10 parts by weight of a p-diazo diphenylamine salt,

(b) adding the mixture in portions to about 50 parts by weight concentrated sulfuric acid while maintaining the temperature below about 5 C.,

(c) subsequently contacting the reaction mixture with an ice-water mixture containing a substantial excess of cadmium chloride, biased on the weight of diazonium salt employed, to precipitate the cadmium salt of the resin,

(d) forming a slurry by mixing the reaction mixture from (c) with about an equal volume of a lower allcanol to further force the cadmium salt of the resin from solution,

(e) separating the solids from the liquid portions of the slurry from (d),

(f) forming a second slurry by suspension of the solids from (e) in water,

(g) adding barium chloride to the slurry from (f) to convert any residual sulfate which may be present to insoluble barium sulfate,

(11) Separating the liquid from the solid portion of the slurry from (g),

(i) washing the solid residue from (h) with a solution of hydrogen fluoride to precipitate any residual barium which may be present as barium fluoride,

(j) separating the solids from the liquids from step (i),

(k) extracting the solid portion from (j) with water to dissolve the cadmium salt of the resin and thereby separate the resin salt from the barium sulfate and barium fluoride which may be present,

(1) adding an excess, based on the weight of resin salt, of cadmium chloride to the solution from (k) to force the cadmium salt of the resin from the solution as a precipitate,

(m) Washing the cadmium salt of the resin with a lower alkanol to reduce the water content, and

(n) drying the cadmium salt of the resin.

2. A process according to claim 1 wherein the lower alkanol is isopropanol.

3. In a process for separating a stable salt of a lightsensitive diazo resin from an aqueous solution containing the resin and a strong acid, said resin being formed by an intimate mixture of a paradiazodiphenyl amine with an aldehyde being added to concentrated sulfuric acid, the steps comprising:

(a) treating the resin solution with suflicient cadmium chloride to precipitate a cadmium salt of the resin,

(b) treating the resultant mixture with excess barium chloride, based on the amount of sulfate present in the mixture, to precipitate out the sulfate,

(b) filtering the reaction mixture to separate the precipitates including the cadmium salt of the resin and the barium sulfate from the liquid residue,

(b) washing the filtered solids with hydrogen fluoride to convert any residual barium ions to insoluble barium fluoride, and

(c) separating the cadmium salt of the resin from the remaining solids with a suitable solvent.

4. In a process for isolating a stable salt of a lightsensitive, water soluble diazo resin from a resin solution containing said water soluble diazo resin and sulfuric acid, the steps comprising:

(a) treating said resin solution with cadmium halide to thereby form the cadmium salt of said diazo resin,

(b) treating the resulting mixture of resinous cadmium salts with an excess, based on the amount of said sulfuric acid present, of water-soluble barium salt to thereby form barium sulfate,

(c) separating a mixture containing (i) said cadmium 'Salt of said diazo resin and (ii) said barium sulfate, from the reaction mixture of step (b),

(d) washing the separated mixture of salts with sufficient hydrogen fluoride to convert any excess watersoluble barium salt in said separated mixture of salts to barium fluoride, and

(e) thereafter separating said cadmium salt of said diazo resin from the resulting mixture.

References Cited UNITED STATES PATENTS 2,679,498 5/1954 Seven et al 260-725 2,714,066 7/1955 Jewett et al. 96-27 3,163,633 12/1964 Steppan et a1. 260-141 3,235,382 2/1966 Neugebauer et al. 260-725 3,246,986 4/1966 Borchers 260-72 WILLIAM H. SHORT, Primary Examiner.

E. M. WOODBERRY, Assistant Examiner.

US. Cl. X.R. 96-91 

